Connecting rod offset

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Rob Habets
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Connecting rod offset

Post by Rob Habets » Tue Feb 17, 2015 7:23 am

Hi,
i got myself a set of AA-connecting rods, but they seem to have no offset, like oem rods?
What's the right way to mount them?
Regards, Rob

Steve Arndt
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Re: Connecting rod offset

Post by Steve Arndt » Tue Feb 17, 2015 10:45 am

Bearing tangs pointing down is customary.

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Marc
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Re: Connecting rod offset

Post by Marc » Tue Feb 17, 2015 2:59 pm

If the rods do in fact have zero offset, it makes no difference. I make a habit of checking aftermarket rods by placing them on a flat surface, pressing the small end down squarely and observing the gap under the big end...flip over and repeat, if there's any offset this'll show it.
Most aftermarket rods have no (intentional) offset, but if there's even a tiny bit my philosophy is that it shouldn't be in the opposite direction of a stock rod :)

Some rods (like old 356) didn't have the tanged ends together - they were 180° apart and facing the same direction. On that type you could make a case for orienting them by the direction of rotation; but on the vast majority of rods that's not a consideration. The "tangs down" convention is just that - a convention. If there was any other characteristic of the rod that wasn't symmetrical, this would make two of them "right" and two of them "wrong" when you consider rotation of the crankshaft. In the case of rods which are drilled to squirt oil onto the cylinders or pistons, you'd most likely want them to spit on the thrust side so that could be the primary concern, overriding convention.

The Newf
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Re: Connecting rod offset

Post by The Newf » Tue Feb 17, 2015 3:32 pm

Marc wrote:If the rods do in fact have zero offset, it makes no difference. I make a habit of checking aftermarket rods by placing them on a flat surface, pressing the small end down squarely and observing the gap under the big end...flip over and repeat, if there's any offset this'll show it.
Most aftermarket rods have no (intentional) offset, but if there's even a tiny bit my philosophy is that it shouldn't be in the opposite direction of a stock rod :)

Some rods (like old 356) didn't have the tanged ends together - they were 180° apart and facing the same direction. On that type you could make a case for orienting them by the direction of rotation; but on the vast majority of rods that's not a consideration. The "tangs down" convention is just that - a convention. If there was any other characteristic of the rod that wasn't symmetrical, this would make two of them "right" and two of them "wrong" when you consider rotation of the crankshaft. In the case of rods which are drilled to squirt oil onto the cylinders or pistons, you'd most likely want them to spit on the thrust side so that could be the primary concern, overriding convention.
If I understand your post correctly,I think you may have misunderstood offset:Look at this ....

hxxp://www.powayusd.com/teachers/kfaverty/Mech10.pdf

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Marc
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Re: Connecting rod offset

Post by Marc » Tue Feb 17, 2015 3:51 pm

Are you alluding to piston pin offset (p192 of that document)? That's built into the piston, not the rod...if it were to be built into the rod, I refer you to my comment that orienting all four rods the same way would make two of them wrong.

The Newf
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Re: Connecting rod offset

Post by The Newf » Tue Feb 17, 2015 3:55 pm

No...I'm familiar with major/minor thrust side with relation to pin bore offset.

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Marc
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Re: Connecting rod offset

Post by Marc » Tue Feb 17, 2015 4:03 pm

Then I don't see what the misunderstanding's about.

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fastback
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Re: Connecting rod offset

Post by fastback » Tue Feb 17, 2015 4:47 pm

the WBX rods small end is offset "sidweays" since the vertical centerline of the cylinders does not align with the centerline of the rod journals on the crank.
like marc points out regarding rod position when assembling the rods on the crank.
aftermarket H-beam rod's are typically no offset (maybe your AA rods also) , so the small end does' not come in center of the piston

there is also ofset in the piston "the other way" to minimise piston skirt wear

The Newf
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Re: Connecting rod offset

Post by The Newf » Tue Feb 17, 2015 4:59 pm

Sorry...I misunderstood what he was trying to say.

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